The present invention relates to an optical switch and, more particularly, to an optical switch of the type wherein a mirror upstanding on a movable electrode plate is brought out of and into the optical path between opposed end faces of output and input optical fibers by electrostatic driving of the movable electrode plate to perform an ON-OFF operation.
A conventional optical switch will be described below with reference to FIGS. 1A and 1B. FIG. 1A is a top plan view of the optical switch and FIG. 1B a sectional view taken along the line 1Bxe2x80x941B in FIG. 1A.
Reference numeral 20 denotes a movable electrode plate 20 integrally formed with a silicon (Si) substrate through frame-shaped flexure portions 21, and 41 denotes a mirror formed on the top of the movable electrode plate 20. The movable electrode plate 20, the flexure portions 21 and the substrate 10 are formed as an integral whole by subjecting a rectangular starting silicon substrate to thin-film forming, photolithographic and etching process steps. Reference numeral 10a denotes a hole formed through the substrate 10. A brief description will be given of how to manufacture the conventional optical switch. The manufacture begins with the preparation of the substrate 10 whose thickness is hundreds of micrometers. The next step is to form a movable electrode plate (20) formation area in middle of the substrate surface and flexure part (21) formation areas on both sides thereof through application of thin-film forming, photolithographic and etching techniques to the top surface of the substrate 10, followed by forming the mirror 41 in the movable electrode plate (20) formation area through photolithography and etching, and then by selectively etching away the substrate 10 from underneath to form the through hole 10a, providing the movable electrode plate 20 and the flexure portions 21.
Following this, a stationary electrode plate 23 is attached to the underside of the substrate 10 over the through hole 10a in opposing relation to the movable electrode plate 20. A voltage is applied across the movable and stationary electrode plates 20 and 23 to generate electrostatic force, by which the movable electrode plate 20 is driven toward the stationary electrode plate 23.
Now, a description will be given of spatial optical path switching by the above optical switch. FIGS. 1A and 1B show that light transmitted through an output optical fiber 34 and emitted from its emitting end face is reflected by the mirror 41 and impinges on an input optical fiber 35 as indicated by LR. This state will hereinafter be referred to as a steady state. With voltage application across the movable and stationary electrode plates 20 and 23, electrostatic force is generated to attract the both electrodes toward each other, by which the movable electrode 20 is driven and hence displaced downward with the flexure portions 21 deformed accordingly. With the downward displacement of the movable electrode plate 20, the mirror 41 formed on the top of the movable electrode plate 20 is also displaced downward and brought out of the optical path of the light beam emitted from the output optical fiber 34. As a result, the light beam emitted from the optical fiber 34 travels in a straight line and directly impinges on an input optical fiber 35xe2x80x2 as indicated by LS.
The optical switch depicted in FIGS. 1A and 1B is provided with one output optical fiber 34 and two input optical fibers 35 and 35xe2x80x2, and the incidence of light on the both input optical fibers is controlled reversely relative to each other; that is, when the emitted light beam is incident on the one input optical fiber, no light beam is incident on the other, whereas when the light is incident on the latter, no light is incident on the former.
FIGS. 2A to 2D depict operations of a 2-by-2 optical switch of the type having two output optical fibers 34, 34xe2x80x2 and two input optical fibers 35, 35xe2x80x2. The light beam emitted from the output optical fiber 34 is, in the steady state shown in FIGS. 2A and 2B, reflected by the mirror 41 on the movable electrode plate 20 and is incident on the input optical fiber 35. On the other hand, a light beam emitted from the output optical fiber 34xe2x80x2 is, in the steady state of FIGS. 2A and 2B, reflected by the mirror 41 and is incident on the input optical fiber 35xe2x80x2.
In a driven state shown in FIGS. 2C and 2D in which a voltage is applied across the movable and stationary electrode plates 20 and 23 to attract the movable electrode plate 20 toward the stationary electrode plate 23, the light beam emitted from the output optical fiber 34 travels in a straight line over the mirror 41 and impinges on the input optical fiber 35xe2x80x2 but does not strike on the other input optical fiber 35. On the other hand, the light beam emitted from the output optical fiber 34xe2x80x2 travels in a straight line over the mirror 41 and impinges on the input optical fiber 35 but does not strike on the other input optical fiber 35xe2x80x2.
In the above prior art examples there is formed on the movable electrode plate 20 only one mirror 41 which reflects or does not reflect incident light beams. Incidentally, since the mirror 41 has a certain thickness, perfect coincidence of the optical axes of incident and reflected light beans is impossible as described below with respect to FIGS. 3A and 3B. FIG. 3A shows that the light beam emitted from the output optical fiber 34 is reflected by the one surface of the mirror 41 for incidence on the input optical fiber 35 or travels in a straight line over the mirror 41 for incidence on the input optical fiber 35xe2x80x2. In this state, if the optical axis of the optical fiber 34xe2x80x2 is adjusted for coincidence or alignment between the optical axis of the light beam emitted from the output optical fiber 34xe2x80x2 and traveling in a straight line over the mirror 41 and the optical axis of the input optical fiber 35, the optical axis of the light beam emitted from the output optical fiber 34xe2x80x2 and reflected by the other surface of the mirror is displaced out of alignment with the optical axis of the input optical fiber 35xe2x80x2.
Referring next to FIG. 3B, in the illustrated state in which the optical axes of the input optical fibers 35 and 35xe2x80x2 are aligned with the optical axes of the reflected and the straight-line traveling versions of the light beam emitted from the output optical fiber 34, if the optical axis of the optical fiber 34xe2x80x2 is adjusted for coincidence or alignment between the optical axis of the light beam emitted from the output optical fiber 34xe2x80x2 and reflected by the other surface of the mirror 41 and the optical axis of the input optical fiber 35xe2x80x2, the optical axis of the light beam emitted from the optical fiber 34xe2x80x2 and traveling in a straight line over the mirror 41 for incidence on the optical fiber 35 is displaced out of alignment with the optical axis of the input optical fiber 35 as shown.
Thus, the use of only one mirror 41 formed on the movable electrode plate 20 permits implementation of the 1-by-2 optical switch as depicted in FIGS. 1A and 1B, but such a single-mirror structure cannot be applied to the 2-by-2 optical switch because of the displacement of optical axes as referred to above with reference to FIGS. 2A to 2D or FIGS. 3A and 3D. In general, the incidence of light on one mirror from two optical fibers along optical axes crossing at right angles gives rise to the problem of misalignments of optical axes as depicted in FIGS. 3A and 3B. This problem arises also in the case of using, in combination, configurations that enable plural optical beams to impinge on each mirror.
Further, since the thickness of the mirror 41, the accuracy of the position of the mirror 41 on the movable electrode plate 20 and the accuracy of the angle of the mirror surface all exert influence on the axial alignment of the reflected light, it is not easy to achieve accurate axial alignment between the mirror 41 and the output optical fibers 34, 34xe2x80x2 and the input optical fibers 35, 35xe2x80x2.
It is therefore an object of the present invention to provide an optical switch that is free from the above-mentioned problem of misalignment between optical axes and has mirrors so arranged as to facilitate alignment between them and input optical fibers.
The optical switch according to the present invention comprises:
a substrate;
a stationary electrode plate provided on said substrate in parallel relation thereto;
a movable electrode plate mounted on said substrate through flexure portions and in space parallel relation to said stationary electrode plate so that said movable electrode plate moves toward or away from said stationary electrode plate;
a first optical fiber having an optical axis on a first straight line passing across said movable electrode plate in parallel relation to said substrate and having its first light beam emitting tip end portion fixed to said substrate;
a second optical fiber having an optical axis on a second straight line passing across said movable electrode plate in parallel relation to said first straight line and having its tip end portion fixed to said substrate;
a first mirror formed on said movable electrode plate, for reflecting said first light beam emitted from said first optical fiber to a direction across said second straight line; and
a second mirror formed on said movable electrode plate, for reflecting said reflected light beam from said first mirror as a second light beam along said second straight line for incidence on the end face of said tip end portion of said second optical fiber fixed to said substrate;
wherein said movable electrode plate moves toward or away from said stationary electrode plate in response to the application of a voltage across said movable electrode plate and said stationary electrode plate or removal of said voltage from between said movable and stationary electrode plates by which said first and second mirrors are brought out of or into the paths of said first light beam and said reflected light beam from said first mirror.